The present invention relates to a protective relay apparatus and a power switchboard.
Conventional protective relay apparatus and power switchboard are configured of protection/instrumentation control units for converting current or voltage signals delivered from a transformer having several kinds of primary rated current ratios or one kind of primary rated voltage ratio into appropriate voltage signals by using a gain control section in front of an operational amplifier and for subjecting them to operational processing after A/D conversion.
The conventional art cited above involves the problem in that detectable errors within the detectable range of protection and instrumentation cannot be assessed on account of a relationship taking account of a detectable range of an input circuit for inputting an analog current or voltage signal and errors of transformer input circuits, and a current signal or a voltage signal, which is transmitted from the transformer, is assigned to each input circuit.
While there was the gain control section in front of the operational amplifier to be compatible with a transformer having several kinds of rated current or voltage ratios, there also was the further problem that this gain control section not only was expensive but also required a large mounting area.
To solve the above-mentioned problems, it is an object of the present invention to provide a protective relay apparatus and a power switchboard which are capable of detecting a current or a voltage without a gain control section in front of an operational amplifier.
To accomplish the object, according to a first aspect of the present invention, there is provided a protective relay apparatus having a transformer for outputting a detection signal in accordance with the varying current or voltage of a main circuit and a control unit for determining that the main circuit is in a predetermined state by using the detection signal and outputting a control signal for switching on/off the main circuit, comprising: an input circuit comprising an operational amplifier for inputting the detection signal and an A/D converter for A/D converting an output signal from the operational amplifier; control means for inputting an output signal from the input signal, determining that the main circuit is in the predetermined state, and outputting a control signal for switching on/off the main circuit; and means comprising a plurality of the input circuits, for setting detectable ranges of the plurality of input circuits for each of the plurality of input circuits.
Further, according to a second aspect of the present invention, there is provided a protective relay apparatus having a transformer for outputting detection signals in accordance with the varying current or voltage of a main circuit, an input circuit comprising an operational amplifier for inputting the detection signal and an A/D converter for A/D converting an output signal from the operational amplifier, and a control unit for inputting an output signal from the input signal, determining that the main circuit is in the predetermined state, and outputting a control signal for switching on/off the main circuit, comprising: setting means for setting a detectable range of the input circuit, wherein the setting means displays a detection state of the input circuit based on a relationship between the detectable range of the input circuit and a detectable error.
Furthermore, according to a third aspect of the present invention, there is provided a protective relay apparatus having a transformer for outputting a detection signal in accordance with the varying current or voltage of a main circuit, an operational amplifier for inputting the detection signal, an input circuit having an A/D converter for A/D converting an output signal from the operational amplifier and a control unit for inputting an output signal from the input signal, determining that the main circuit is in the predetermined state, and outputting a control signal for switching on/off the main circuit, comprising: setting means for setting a detectable range of the input circuit, wherein the setting means displays the detection state of the input circuit based on a relationship between the detectable range of the input circuit and a reference value of a detectable error.
In addition, according to a fourth aspect of the present invention, there is provided a protective relay apparatus having a transformer for outputting a detection signal in accordance with the varying current or voltage of a main circuit and a control unit for determining that the main circuit is in a predetermined state by using the detection signal and outputting a control signal for switching on/off the main circuit, comprising: a first input circuit comprising a first operational amplifier for inputting the detection signals and an A/D converter for A/D converting an output signal from the first operational amplifier; and a second input circuit comprising a second operational amplifier for inputting the detection signal, which has gain characteristics compatible with wide range detection permitting detection in a wide varying range of a current or a voltage, as compared with the first operational amplifier, and an A/D converter for A/D converting an output signal from the second operational amplifier, wherein each of the first and second circuits comprises means for setting the detectable range thereof, and the detectable ranges are figured out by an arithmetic expression on the basis of the magnitude of the error of each of the first and second input circuits, resolving power of the A/D converter, and the tolerable detectable errors of the instrumentation.
According to the present invention, by using the above-mentioned means, it is possible to provide compact, light-weight and inexpensive protective relay apparatus and power switchboard which are improved in accuracy of instrumentation.
To accomplish the object, for the purpose of evaluating detectable errors within the detectable range of protection and instrumentation, the present invention has derived an arithmetic expression having, as its parameters, the magnitude of any error of a transformer input circuit or a current transformer input circuit, a resolving power of the A/D converter, an effective amperage (voltage) and the detectable range of the transformer input circuit or the current transformer input circuit containing the operational amplifiers.
Further, by setting the detectable range of the input circuit containing the operational amplifiers, which is a parameter of the arithmetic expression, the configuration is made compatible with a transformer having several kinds of rated current ratios or rated voltage ratios and one kind of primary rated current ratio or primary rated voltage ratio.
This makes it possible to manufacture a transformer which can have several kinds of rated current ratios or rated voltage ratios and a protective relay apparatus and a power switch board compatible with the current transformer.